Generally, an indoor lighting device using an LED can be roughly classified into a bulb-type lighting device which is to replace a socket-type light bulb and a surface lighting device which is to replace a fluorescent light.
Among them, most surface lighting devices use a diffusion plate having a predetermined area as a cover, and an example thereof is disclosed in Korean Patent No. 10-0998980 (registered on Dec. 1, 2010). In FIG. 4 which is a representative drawing of the registered patent, a substrate on which a plurality of LEDs are arranged to upwardly emit light is packaged, and a diffusion layer of one or more layers is included on the substrate, so that light emitted from the plurality of LEDs is diffused, thereby illuminating the entirety of a surface having a specific size at a constant illuminance.
The above-described configuration, which is commonly used as a general surface lighting device, has a problem in that the diffusion plate prevents light from being intensively emitted from a part thereof, so that glare is prevented from being generated, but light efficiency is reduced due to a large amount of optical losses.
For this reason, there is a problem in that, since a larger number of LEDs than necessary should be used in order to provide a surface light source having a sufficient illuminance, an advantage of a LED light, which corresponds to low power consumption, can be weakened, and since it is not easy to treat emitted heat, the lifespan of the LED can be shortened due to the heat.
In addition, in a case of a surface light emitting device illustrated in FIG. 4 of the Patent, there is a problem in that the design of a case should necessarily be changed when the lighting device is changed from a 40 W type to a 20 W type under an assumption that LEDs chip having the same output are used.
In this case, when 20 W LEDs are used, the number of LEDs is decreased to the half number of 40 W LEDs, so that an interval between the LEDs is widened. As a result, a bright area and a dark area are generated on the diffusion plate directly under a light emitting surface of the LEDs, so that illumination unevenness of a light emitting surface is generated.
There is a problem in that, in order to resolve such illumination unevenness, a design change should be made in which a distance between the LED and the diffusion plate is adjusted to be wider, or a light emitting part should be actually manufactured in a half size and a reflector, etc. should be employed as the other half part.
In addition, since the fluorescent lamp type LED lighting devices according to the related art have a light-emitting surface facing the bottom surface, and have a limited light emitting angle with regard to the light-emitting surface, a dark zone darker than surroundings thereof exists on a ceiling near the lighting devices.
There is a problem in that the forming of such a dark zone causes a feeling that it is darker than an actual indoor brightness, and the illumination unevenness causes a disorganized and distracted indoor atmosphere.